1. Field of the Invention
The present invention relates to an inkjet recording apparatus employing a line head.
2. Description of the Related Art
Conventionally, in a recording head used in an inkjet recording apparatus, it has been necessary to reduce wasteful consumption of ink discharged from the recording head to continuously stabilize the ink discharge condition even when printing is continuously performed on a large number of sheets. To stabilize the ink discharge condition, it is important to stabilize the temperature of the recording head. In view of this, there is adopted an ink circulation structure for controlling the temperature of ink supplied to the recording head, to return ink supplied to the recording head from the recording head to an ink tank unit, and controlling the temperature of ink again, to supply ink to the recording head.
Japanese Patent Application Laid-Open No. 11-10908 discusses a configuration equipped with a flow path for circulating ink between a recording head and an ink tank, a pump provided in the flow path, and a temperature sensor configured to detect the temperature of the recording head, so that the ink circulation supply amount can be controlled based on the temperature detected by the temperature sensor.
Japanese Patent Application Laid-Open No. 2008-23806 discusses a configuration equipped with a circulation for circulating ink between a recording head and an ink tank, and a pump and a temperature detection unit provided in the circulation route, so that the ink temperature and the ink circulation flow rate in the circulation flow path can be variably controlled.
In a recording head used in an inkjet recording apparatus for a large-volume, high-speed, and continuous printing apparatus as used in a print laboratory, there is known a line head on which a plurality of nozzle chips are arranged in a zigzag fashion.
The nozzle chip portions are formed by utilizing a semiconductor device production method. At the chip portions thereof, there are formed discharge ports through which ink is discharged, energy generation elements for discharging ink, thermistor elements for detecting the temperature of the chip portions, etc.
In a recording apparatus using this line head, a recording medium is continuously conveyed, and recording is performed at the point when the recording medium reaches the ink discharge position of the line head. If the ink circulation mechanism and the recording head temperature control method according to Japanese Patent Application Laid-Open No. 11-10908 and Japanese Patent Application Laid-Open No. 2008-23806 are applied to the line head, the following problem will arise.
The line head has a length equal to or larger than the width of the recording medium. Thus, as illustrated in FIG. 12, when ink is supplied to the ink circulation flow path inside the line head that performs a recording operation, ΔT1 (° C.) which indicates a difference in chip portion temperature between the ink supply port side and the discharge port side of the line head becomes very large. When the difference in temperature increases, the variation in ink droplet discharge size and in ink discharge amount will increase. This involves an image quality problem with an increasing difference in ink density between both ends of the recording medium.
It may be possible to diminish the difference in temperature between the supply port side and the discharge port side of the line head by increasing the amount of ink that is allowed to pass through the inside of the line head. However, if a certain of amount or more of ink flows into the line head, a discharging operation may be affected. The pump and the circulation flow path may also suffer damage. Further, from the viewpoint of energy saving, there is a requirement to suppress the ink flow rate as low as possible.